Process for preparing esters of unsaturated alcohols

ABSTRACT

A process for the catalytic dehydration of saturated 2,2,4-trisubstituted glycol monoesters at elevated temperatures to unsaturated 2,2,4-trisubstituted monoesters in the presence of a non-volatile acid catalyst.

FIELD OF THE INVENTION

This invention relates to a process for preparing esters from saturatedalcohols. More specifically it pertains to a continuous process forpreparing esters of unsaturated alcohols by the catalytic dehydration of2,2,4-trisubstituted glycol monoesters.

DESCRIPTION OF THE PRIOR ART

The process for producing esters of unsaturated alcohols from monoestersof saturated 2,2,4 trisubstituted-1,3-diols has long been known and waspatented by Hagemeyer et al. in U.S. Pat. No. 3,408,388 on Oct. 29,1968. The process disclosed in this patent involves contacting a glycolmonoester with a highly acidic, nonvolatile catalyst at a temperature inthe range of from about 90° C. to about 160° C. to cause dehydration andformation of the corresponding ester of an unsaturated2,2,4-trisubstituted alcohol. The acidic catalysts useful are discussedin column 3, lines 20-25, column 4, line 73 to column 5, line 13 and inclaim 1 at column 11, lines 1 to 5 of U.S. 3,408,388. In thisdiscussion, the patentees, at column 5, lines 8 to 13, specificallystate, concerning the suitable catalysts, that "The members of the groupof specific dehydration catalysts are somewhat exclusive in effectinasmuch as other nonvolatile compounds such as potassium acidsulfate--are not effective under the conditions of this invention."Thus, the patentees have taken the positive position, apparently basedon their experiences with their process, that potassium acid sulfate isnot a catalyst for the dehydration of the defined saturated glycolmonoesters to the corresponding esters of unsaturated2,2,4-trisubstituted alcohols. In addition, this patent reference alsoteaches that the dehydration should be carried out at a temperaturerange substantially from 90° C. to 160° C. with the optimum range beingsubstantially from 110° C. to 135° C. and presents a detailed discussionof the disadvantages of operating outside the defined broad range. Itstates that at "a dehydration temperature above 160° C., the dehydrationof the glycol monoester is nearly complete but the principal products ofthe reaction include the ester of the unsaturated alcohol, the acid,substituted tetrahydrofurans and other products which are formed by aninitial cracking or rearrangement reaction". The patentees are clearlyadvising the industry that a temperature above 160° C. is to be avoidedand unsatisfactory and leads to considerable undesired quantities ofmany by-products. The teachings in U.S. Pat. No. 3,408,388 arecompletely contrary to what was found by the inventors of this instantpatent application, both as to temperature and products, as will be seenbelow. The patentees' discussion in U.S. Pat. No. 3,408,388 ontemperature is found at column 5, lines 29 to 46.

British Patent Specification No. 1,288,615, published Sept. 13, 1972,issued to Bertram Yeomans and assigned to BP Chemicals Ltd., relates tothe production of 2,2,4-trimethylpentanol-1. In the process one stepinvolves the dehydration of 3-hydroxy-2,2,4-trimethylpentyl-1isobutyrate to 2,2,4-trimethylpentenyl isobutyrate. This dehydration iscarried out by heating the saturated ester in contact with an acidcatalyst, at 90° C. to 300° C., together with an entrainer for theazeotropic removal of water for a period of 5 to 50 hours, preferably 12to 36 hours (page 2, lines 13 to 37). Example 1 (page 2, lines 87 to100) and Example 2 illustrate this azeotropic procedure. Though productis obtained the selectivity to 2,2,4-trimethylpentenyl isobutyrate isrelatively low; in Example 1 it is about 83% and Example 2 shows valuesof 62% and 57% for two of the three experiments. These selectivities areconsiderably lower than those obtained by the instant applicants.Further, applicants' process does not require the entrainer and theaverage contact time in the reaction is less.

British Patent Specification No. 1,290,094, published Sept. 20, 1972,issued to Bertram Yeomans and assigned to BP Chemicals Ltd., relates tothe transesterification of 2,2,4-trimethylpentane- 1,3-diol with2,2,4-trimethylpentyl-1 isobutyrate in the presence of a metal,alkoxide, oxide or hydroxide of a metal of a main group element of GroupI or Group II of the Periodic Table to produce2,2,4-trimethylpentanol-1. In the description of the process anintermediate dehydration step is disclosed (page2, lines 29 to 87) fordehydrating hydroxy-2,2,4-trimethylpentyl-1 isobutyrate in admixturewith added 2,2,4-trimethylpentyl-1,3- diisobutyrate (with the dibutyrateester content in the reaction preferably being greater than 30 weightpercent) to the unsaturated 2,2,4-trimethylpentenyl-1 isobutyrate. Thisis stated as being accomplished using an acid catalyst at 120° C. to200° C. over a reaction time of from 20 to 60 hours preferably 30 hours(page 2, lines 82-83). The reference requires deliberate addition of thediester (page 2, lines 53-54 and lines 63-78).

SUMMARY OF THE INVENTION

A process for the production of unsaturated 2,2,4-trisubstitutedmonoesters by the catalytic dehydration of a saturated2,2,4-trisubstituted glycol monoester in contact with a catalytic amountof non-volatile acid catalyst at a reactor temperature of from about170° C. to about 270° C.

DESCRIPTION OF THE INVENTION

This invention provides a continuous process for dehydrating saturated2,2,4-trisubstituted glycol monoesters of general formula I, hereinaftershown, to unsaturated 2,2,4-trisubstituted monoesters of generalformulas II and III, hereinafter shown, in high yield rate andconversion at yields approaching 95 percent under conditions that werenot heretofore considered capable of producing the unsaturatedmonoesters. In the process of this invention it was found thattemperatures and catalysts heretofore considered unsuitable for thedehydration of the saturated 2,2,4 trisubstituted glycol monoesters totheir corresponding unsaturated 2,2,4-trisubstituted monoesters can beused in a continuous process to obtain the desired unsaturated productin high yield. The present invention does not require deliberateaddition of entrainer or diester.

In the condensation of aldehydes to their corresponding saturated2,2,4-trisubstituted glycol monoesters, the product obtained isgenerally a mixture of two isomers having the formulas IV and V:##STR1## This condensation reaction is well known and fully documentedin U.S. Pat. No. 3,091,632 (Hagemeyer et al., May 28, 1963), U.S. Pat.No. 3,291,821 (Perry et al., Dec. 13, 1966) and U.S. Pat. No. 3,718,689(McCain et al., Feb. 27, 1973) all of which describe various catalyticmethods for their production and uses for these compounds.

An important use for these saturated compounds is as the startingmaterials for the unsaturated 2,2,4-trisubstituted monoesters, which areobtained by an acid catalyzed dehydration reaction. The dehydration ofisomeric mixtures of IV and V yields a mixture of unsaturated2,2,4-trisubstituted monoesters of formulas II and III: ##STR2##However, unless care is taken in conducting the reaction, considerablelosses can be sustained by formation of unwanted by-products. Forexample, disproportionation of compounds IV and V can result in theformation of the diester: ##STR3## in Which both R" groups are --OCR'groups and the diol: ##STR4## Though the diester is relatively stable,the diol dehydrates rapidly to the unsaturated alcohols: ##STR5## whichpreferentially cyclize to 2,2,4,4-tetrasubstituted tetrahydrofurans:##STR6## In addition, during the reaction the unsaturated alcohol willundergo dehydration leading to a complex mixture of C-8 dienes and otherorganic lights. Thus, the avoidance or minimization of the formation ofdiester, diol, unsaturated alcohol, furan and other by-products in anysignificant amount is desirably avoided. The process of this inventiondoes so to a high degree since conversions as high as 95% or more to thedesired products II and 111 are achieved. The variables R, R' and R" arehereinafter defined.

It was noted that during startup, the inefficiency to undesiredby-product might be higher than desired. However, as the reactionproceeded by-product formation was inhibited and significantly reduced,resulting in conversions to desired unsaturated 2,2,4-trisubstitutedmonoesters at high rates and high yields or selectivity of 90% to 95% orhigher.

In the process of this invention the saturated 2,2,4-trisubstitutedglycol monoester of the general formula: ##STR7## are catalyticallydehydrated at elevated temperature to the unsaturated2,2,4-trisubstituted monoesters of the formulas: ##STR8## Subgeneric toFormula I are compounds of the formulas: ##STR9##

In Formulas I to V the R, R' and R" groups have the following meanings:

R is hydrogen or an unsubstituted or substituted hydrocarbyl group thatcan be (i) an alkyl group having from 1 to about 8 carbon atoms,preferably 1 to 4 carbon atoms, (ii) a cycloalkyl group having 5 or 6ring carbon atoms, or (iii) an aryl, alkaryl or aralkyl group in whichthe aromatic ring is either phenyl or naphthyl;

R' is a hydrocarbyl group as defined for R; and

R" is (i) hydrogen or (ii) an --OCR group with the proviso that inFormula I one of the R' groups is hydrogen and in Formulas I to V an--OCR' group is always present.

Compounds of these formulas are well known and many are readilyobtainable. The saturated 2,2,4-trisubstituted glycol monoesters areeasily synthesized by the process described in U.S. Pat. No. 3,091,632by the trimeric condensation of the alpha, alpha-disubstitutedacetaldehydes. Illustrative of saturated 2,2,4-trisubstituted glycolmonoesters are 3-hydroxy-2,2,4-trimethylpentyl isobutyrate,3-hydroxy-2-ethyl-2,4 dimethylhexyl 2-methylbutyrate, 3-hydroxy2,2,4-triethylhexyl 2-methylbutyrate, 3-hydroxy 2,2,4-trimethylpentylacetate, 2-ethyl-3-hydroxy-2,4-dimethylhexyl 2-methylbutyrate,2-butyl-2,4-diethyl-3 hydroxyoctyl 2-ethylhexanoate,2,4-diethyl-3-hydroxy-2-isobutylheptyl 2-ethyl-4methylpentanoate,3-hydroxy-2,2,4-triethylhexyl 2-ethylbutyrate,2-cyclohexyl-3-hydroxy-2,4-dimethylhexyl 2-cyclohexylpropionate,3-hydroxy-2,2,4-tricyclohexylbutyl 2,2-dicyclohexylacetate,2-methyl-3-hydroxy-2,4-di(para-methylphenyl)pentyl2(para-methylphenyl)propionate,1-hydroxy-2,2,4-trimethylpentyl-3-isobutyrate,1-hydroxy-2-ethyl-2,4-dimethylhexyl 3(2-methylbutyrate), 1-hydroxy2,2,4-triethylhexyl 3(2-methylbutyrate), 1-hydroxy-2,2,4 trimethylpentyl3-acetate.

The dehydration of the 2,2,4-trisubstituted glycol monoesters ofFormulas I, IV and V is readily carried out at elevated temperature inthe presence of a catalytic amount of the catalyst sufficient to carryout the dehydration reaction.

The dehydration reaction is carried out in this process at a reactionkettle temperature of from about 170° C. to about 270° C., preferablyfrom about 180° C. to about 250° C. The reaction is preferably carriedout in a continuous manner and is compatible with operation in a stillwith addition of reactants and catalyst to the kettle and continuousremoval of unsaturated ester overhead and water of reaction decanted.The column temperature can be controlled by varying the kettletemperature, feed rate, pressure and reflux ratio under which thedehydration reaction is being conducted. The size of the distillationcolumn, the volume of material passing through the column and thetemperature of the coolant also affect the column temperature.

The dehydration is catalyzed using a catalytic amount of a substantiallynon-volatile acid catalyst. Among the suitable catalysts are the weakacids or the strong acids. These are well known to those of ordinaryskill in this art and require no further description here. However, infurther clarification typical of suitable acids one can mention thealkali metal hydrogen sulfates (e.g., sodium hydrogen sulfate andpotassium hydrogen sulfate). p-toluenesulfonic acid (PTSA), sulfuricacid, phosphoric acid, and the like. However, it may be necessary toreplenish the catalyst due to carry over with volatile products, inorder to maintain a catalytic concentration of the catalyst. It wascompletely unexpected and unpredictable that dehydration to the desiredunsaturated 2,2,4- trisubstituted monoesters of Formulas II and III wasachieved in such high yield and rate under the process conditions ofthis invention in view of the statements in U.S. Pat. No. 3,408,388.

In U.S Pat. No. 3,408,388, the reaction conditions specify a temperatureof from 90° C. to 160° C. This reference states that at a dehydrationtemperature above 160° C., the dehydration of the glycol monoester isnearly complete but in addition to the ester of the unsaturated alcohol,the acid, substituted tetrahydrofurans and other products are formed(column 5, lines 34 to 45). The reference also states that potassiumacid sulfate was not effective (column 5, lines 8 to 13). Thus, it wassurprising to find that we could produce the unsaturated2,2,4-trisubstituted monoesters of Formulas II and III in such highyield and rate even by the use of the catalysts sodium hydrogen (acid)sulfate and potassium hydrogen (acid) sulfate. This was completelyunexpected and contra to the teachings in the prior art.

The amount of catalyst charged to the reaction kettle is an amountsufficient to catalyze the dehydration reaction. This amount can be fromabout 0.005 to about 5 weight percent, preferably 0.05 to about 1 weightpercent, most preferably from about 0.1 to about 0.5 weight percentbased on the amount of saturated 2,2,4-trisubstituted glycol monoesterin the reactor. The preferred catalysts are sodium hydrogen sulfate andpotassium hydrogen sulfate at concentrations below about 0.5 weightpercent.

The reaction is carried out at a pressure of about 100 mm Hg or higher,preferably from about 200 mm Hg to about 750 mm. Pressure is notcritical.

It is preferred to maintain as short a contact time as possible in thereactor in order to minimize side reactions. However, this will varydepending upon the size of the reactor and column and the specificreactants and reaction conditions employed.

In general the average contact time of reactants with the non-volatileacid catalysts is from about 0.5 hour or less to about 4.5 hours. Thoughone can use longer contact periods, it is of no significant advantageand may lead to undesireable reactions.

The reaction is typically carried out in a conventional distillationreactor equipped with a multi-tray distilling column. The reactor ischarged with the saturated monoester (e.g. 2,2,4-trisubstituted glycolmonoester) and catalyst and heated to the desired temperature at reducedpressure. When the system has reached reflux, make-up saturatedmonoester is added to the kettle at a feed rate to maintain a constantvolume in the reactor and distillates are removed.

The following examples serve to further illustrate the invention.

EXAMPLE 1

To a 2-liter reaction kettle equipped with a 10-tray Oldershaw columnand a water cooled automatic reflux head there was added 940 g of anisomeric mixture of 1-hydroxy-2,2,4-trimethylpentyl 3-isobutyrate and3-hydroxy-2,2,4 trimethylpentyl isobutyrate and 0.94 g (0.1 wt. %)potassium hydrogen sulfate. This isomeric mixture of monohydroxy-2,2,4-trimethylpentyl isobutyrates is hereinafter referred to as (A).The system was brought to reflux at 150 mm Hg and isomericmonohydroxy-2,2,4-trimethylpentyl isobutyrates (A) was fed to the kettleat the rates shown in Table I.

The column was operated for approximately 10 hours with average feed andmake rates of 250-300 cc/hr. Kettle temperature was approximately 180°C., and reflux adjusted to maintain a head temperature of 115° C. Theproduct efficiency to the mixture of the two2,2,4-trimethylpentenyl-1-isobutyrates (B) isomers was in the 85 to 91%range during this period.

After 10 hours, the kettle was concentrated to half its original level(470 g) to decrease the residence time and increase the acid catalystconcentration. The system was operated under the same conditions for anadditional 10 hours and gave comparable results. During the run, between1.5 and 5.5% monohydroxy-2,2,4 trimethylpentyl isobutyrates (A) wastaken overhead with organic lights and 2,2,4-trimethyl-1,3-pentanediol(D).

The 10-tray Oldershaw column was then replaced with a 30-tray Oldershawcolumn to decrease the amounts of diol (D) andmonohydroxy-2,2,4trimethylpentyl isobutyrates (A) taken overhead withthe product. The system was restarted and operated for approximatelyfive hour periods under the conditions and with the results in Table 1.A stoichiometric amount of water (˜8%) separated from the collectedproduct and was decanted.

                                      TABLE 1                                     __________________________________________________________________________    Reaction                   Make                                               Progress                                                                           Feed Rate                                                                           Pressure                                                                           Reflux                                                                            Temp. (°C.)                                                                   Rate                                                                              Yield                                          (hrs)                                                                              (mL/h)                                                                              (mm Hg)                                                                            Ratio                                                                             Kettle/Head                                                                          (mL/h)                                                                            % B                                                                              % A                                                                              % C                                      __________________________________________________________________________    20-25                                                                              240   145  1:4 185/104                                                                              240 97.5                                                                             0  0                                        26-30                                                                              245   300  2:1 206/127                                                                              245 96.7                                                                             0  0                                        31-35                                                                              330   760  2.5:1                                                                             246/157                                                                              325 95.6                                                                             0  0                                        Kettle                         31.4                                                                             38.6                                                                             26.7                                     Analysis                                                                      __________________________________________________________________________     C: 2,2,4trimethylpentyl 1,3diisobutyrate.                                     Note:                                                                         A portion of this compound is originally present in the charged isomeric      mixture (A).                                                             

Example 1 clearly demonstrates the high efficiency of the process ofthis invention at kettle temperatures higher than those previouslyconsidered suitable for the reaction and use of potassium hydrogensulfate as the catalyst, a material previously published as beingnon-catalytic for this reaction in U.S. Pat. No. 3,408,388.

EXAMPLE 2

This example demonstrates operation of the process of this inventionwith catalyst levels of 0.01 to 0.05 wt. % The reaction system describedin Example 1 (30-tray Oldershaw column) was used to react the isomericmixture of monohydroxy-2,2,4-trimethyl isobutyrates (A). The system wasoperated for approximately five hour periods to produce product (B)under the conditions and with the results for each period described inTable 2.

                                      TABLE 2                                     __________________________________________________________________________    Kettle                                                                             Feed                     Make                                            Level                                                                              Rate                                                                              Catalyst                                                                           Pressure                                                                           Reflux                                                                            Temp (°C.)                                                                    Rate Yield                                      (grams)                                                                            (mL/h)                                                                            (wt. %)                                                                            (mm Hg)                                                                            Ratio                                                                             Kettle/Head                                                                          (mL/h)                                                                             % B                                                                              % A                                                                              % C                                  __________________________________________________________________________    500  95  KHSO.sub.4                                                                         302  5:1 212/128                                                                              95   96.2                                                (0.01)                                                               500  200 KHSO.sub.4                                                                         302  2:1 219/120                                                                              200  97.0                                                (0.03)                                                               670  80  H.sub.2 SO.sub.4                                                                   303  1:1 221/126                                                                              60   89.4                                                (0.01)                                                               670  245 H.sub.2 SO.sub.4                                                                   303  3:1 217/116                                                                              255  96.1                                                (0.05)                                                               Kettle                             11.8                                                                             78.6                                                                             7.0                                  Analysis                                                                      __________________________________________________________________________

In Example 2 it is shown the process of this invention is consistentlyeffective at the higher temperatures and that considerably lowercatalyst concentrations of catalyst can be effectively used.

EXAMPLE 3-a

This example shows operation of the process with p-toluenesulfonic acidmonohydrate as the acid catalyst and demonstrates the sensitivity ofproduct composition to the head temperature as controlled by the refluxratio. The system was operated with the equipment described in Example 2with an initial charge of 1000 g of monohydroxy-2,2,4-trimethylpentylisobutyrates (A) using 0.18 wt. % PTSA.H₂ O. The results of the run aresummarized in Table 3. In hours 2-6 the system was operated with a highhead temperature which resulted in the codistillation of startingmono-esters (A), with the product (B). Lowering the head temperatureduring hours 6-12 to 152° C. by increasing the reflux ratio, eliminatedthe carry over of the monohydroxy-2,2,4-trimethylpentyl isobutyrates (A)starting material.

                                      TABLE 3                                     __________________________________________________________________________    Reaction  Feed       Make                                                     Progress                                                                           Pressure                                                                           Rate                                                                              Temp (°C.)                                                                    Rate Reflux                                                                            Yield                                           (hrs)                                                                              (mm Hg)                                                                            (mL/h)                                                                            Kettle/Head                                                                          (mL/h)                                                                             Ratio                                                                             % B                                                                              % A                                                                              % C                                                                              % D                                    __________________________________________________________________________    2-4  302  590 214/155                                                                              525  2:4 87.1                                                                             9.8                                                                              0  0.8                                    4-6  302  495 214/165                                                                              620  2:5 76.8                                                                             18.6                                                                             0  0.4                                    6-12 302  400 214/152                                                                              415  3:2 97.4                                                                             0  0  0.7                                    Kettle                        15.0                                                                             61.6                                                                             19.5                                                                             1.2                                    Analysis                                                                      __________________________________________________________________________

EXAMPLE 3-b

This example shows operation of the process with the acid catalystutilized in Example 3-a but at a higher level. The results of the runare summarized in Table 4. The system used for this example consisted ofa 40-tray Oldershaw column equipped with a water cooled automatic refluxhead and a 500 cc kettle. The system was charged with 233 g ofmonohydroxy-2,2,4-trimethylpentyl isobutyrates (A) and 0.40 wt. %PTSA.H₂ O. The results during the first hour demonstrate theinefficiency of the process during startup. During the next four hours,the system stabilizes and the efficiency steadily increases to itsnormally high yield level for the production of (B).

                                      TABLE 4                                     __________________________________________________________________________    Reaction  Feed       Make                                                     Progress                                                                           Pressure                                                                           Rate                                                                              Temp (°C.)                                                                    Rate Reflux                                                                            Yield                                           (hrs)                                                                              (mm Hg)                                                                            (mL/h)                                                                            Kettle/Head                                                                          (mL/h)                                                                             Ratio                                                                             % B                                                                              % A                                                                              % C                                                                              % D                                    __________________________________________________________________________    0-1  300   65 193/70-160                                                                            55  1:10                                                                              67.3                                                                             0.9                                                                              1.4                                                                              0.1                                    1-5  302  225 209/161                                                                              255  --  95.4                                                                             0.7                                                                              0.1                                                                              0.9                                    __________________________________________________________________________

EXAMPLE 3-c

This example shows the adverse effect of lower pressure on the reactionrate when a weak acid catalyst such as p-toluenesulfonic acidmonohydrate is utilized. The system was operated as in Example 2 with aninitial charge of 1350 g of monohydroxy-2,2,4-trimethylpentylisobutyrates (A). The level of acid catalyst (PTSA.H₂ O) was varied from0.10 to 0.30 wt. %. During hours 6-25, when the system was operated at300 torr, a good reaction rate was maintained and high yields of product(B) were achieved with 0.10 wt. % catalyst (see Table 5). When thepressure was decreased to 100 torr, the kettle temperature decreasedfrom 215° C. to 188° C., resulting in in a dramatic decrease in reactionrate at a catalyst concentration of 0.10 wt. % (hours 25-32). Evenincreasing the acid level three-fold (from 0.10 to 0.30 wt. %; hours32-39) did not bring the rate back to the level observed when the systemwas operated at 300 torr. However, desired product (B) was stillproduced.

                                      TABLE 5                                     __________________________________________________________________________    Reaction         Feed       Make                                              Progress                                                                           Catalyst                                                                             Pressure                                                                           Rate                                                                              Temp (°C.)                                                                    Rate Reflux                                                                            Yield                                    (hrs)                                                                              (wt. %)                                                                              (mm Hg)                                                                            (mL/h)                                                                            Kettle/Head                                                                          (mL/h)                                                                             Ratio                                                                             % B                                                                              % A                                                                              % C                                __________________________________________________________________________     6-10                                                                              PTSA (0.10)                                                                          302  180 213/143                                                                              190  1:2 97.2                                     10-17                                                                              PTSA (0.10)                                                                          302  240 215/144                                                                              250  2:3 95.0                                     Kettle                               30.0                                                                             52 11.6                               Analysis                                                                      17-25                                                                              PTSA (0.10)                                                                          300  250 215/145                                                                              280  1:3 97.0                                     Kettle                               16.3                                                                             62.3                                                                             17.9                               Analysis                                                                      25-32                                                                              PTSA (0.10)                                                                          100  210 188/--  75      57.0                                                                             39.0                                  32-39                                                                              PTSA (0.30)                                                                          100  215 188/120-130                                                                          195  2:4 92.3                                                                             4.6                                   __________________________________________________________________________

EXAMPLE 4

This example demonstrates operation of the process with sodium hydrogensulfate (NaHSO₄) as the acid catalyst at various pressures. The systemwas operated with the equipment described in Example 2 with an initialcharge of 1000 g of monohydroxy-2,2,4-trimethylpentyl isobutyrates (A)and using 0.10 wt. % NaHSO₄. With the exception of startup (1-3 hours),the reaction is highly efficient (95+%) at all the pressures examined(see Table 6). Even at atmospheric pressure (30-36 hours), the reactionproceeds with a high efficiency and rate to product (B).

                                      TABLE 6                                     __________________________________________________________________________    Reaction  Feed       Make                                                     Progress                                                                           Pressure                                                                           Rate                                                                              Temp (°C.)                                                                    Rate Reflux                                                                            Yield                                           (hrs)                                                                              (mm Hg)                                                                            (mL/h)                                                                            Kettle/Head                                                                          (mL/h)                                                                             Ratio                                                                             % B                                                                              % A                                                                              % C                                                                              % D                                    __________________________________________________________________________    1-3  301  180 192/145                                                                              240  1:1 82.9                                             4-11                                                                              300  255 197/146                                                                              245  2:4 97.0                                                                             0  0  0.3                                    Kettle                        46 37 13                                        Analysis                                                                      12-20                                                                              150  255 188/129                                                                              330  2:4 96.7                                                                             0  0  0.4                                    Kettle                        23.6                                                                             44.8                                                                             24.6                                      Analysis                                                                      21-29                                                                              302  325 207/148                                                                              387  2:3 96.7                                                                             0  0  0.4                                    Kettle                        26.4                                                                             40.7                                                                             25.9                                      Analysis                                                                      30-36                                                                              760  575 253/177                                                                              476  1:1 95.6                                                                             0  0  0.3                                    Kettle                        16.0                                                                             48 28                                        Analysis                                                                      __________________________________________________________________________

EXAMPLE 5

This example demonstrates operation of the process with the catalyst(NaHSO₄) over a longer period of time. The system used for this exampleconsisted of a 40-tray Oldershaw column equipped with a water cooledautomatic reflux head and a 2-liter kettle. The kettle was charged with1500 g of monohydroxy-2,2,4-trimethylpentyl isobutyrates (A) and 0.20wt. % NaHSO₄. The run was performed over a 70 hour period using a totalfeed of 26.2 liters. The column was operated at 300 torr, and thereaction rate and efficiency to product (B) were high (see Table 7)throughout the run. Kettle analyses taken at various intervals showedthat the 2,2,4-trimethylpentyl 1,3-disobutyrate content of the kettlegradually increased throughout the run (from 7.2 to 50.8%) with noobservable adverse effect on the dehydration reaction. It is to be notedthat diester is initally present in trace amount in feed (A) and is alsoformed during the reaction by the process of this invention.

                                      TABLE 7                                     __________________________________________________________________________    Reaction                                                                           Feed                                                                              Total               Make                                             Progress                                                                           Rate                                                                              Feed                                                                              Pressure                                                                           Reflux                                                                            Temp (°C.)                                                                    Rate Yield                                       (hrs)                                                                              (mL/h)                                                                            (mL)                                                                              (mm Hg)                                                                            Ratio                                                                             Kettle/Head                                                                          (mL/h)                                                                             % B                                                                              % D                                                                              % A                                                                              % C                                __________________________________________________________________________    2-4  518  1485                                                                             305  3.5:1                                                                             178/160                                                                              551  95.3                                                                             0.40                                     Kettle                            50.8                                                                             1.31                                                                             36.3                                                                              7.2                               Analysis                                                                      6-8  615  3990                                                                             309  4:3 182/156                                                                              645  94.0                                                                             0.41                                      9-11                                                                              458     303  5:3 184/157                                                                              500  94.1                                                                             0.44                                     11-13                                                                              380  6420                                                                             302  4:3 184/156                                                                              482  94.1                                                                             0.37                                     16-18                                                                              330  7975                                                                             300  3:4 185/158                                                                              402  95.0                                                                             0.28                                     19-21                                                                              327     302  3:5 193/158                                                                              395  95.6                                                                             0.18                                     22-24                                                                              327 10215                                                                             302  3:5 195/158                                                                              402  96.0                                                                             0.33                                     Kettle                            38.9                                                                             0.39                                                                             28.1                                                                             27.4                               Analysis                                                                      27-29                                                                              325     302  3:5 197/158                                                                              428  96.6                                                                             0.38                                     29-31                                                                              327 12310                                                                             303  3:5 199/158                                                                              383  96.8                                                                             0.20                                     Kettle                            32.2                                                                             0.31                                                                             31.6                                                                             30.8                               Analysis                                                                      33-34                                                                              320     300  3:5 197/157                                                                              328  96.1                                                                             0.17                                     35-36                                                                              330 14410                                                                             300  3:5 198/157                                                                              353  97.0                                                                             0.19                                     38-40                                                                              325     302  3:5 198/159                                                                              352  97.1                                                                             0.26                                     40-42                                                                              288 16430                                                                             302  3:6 200/157                                                                              355  96.9                                                                             0.24                                     Kettle                            28.8                                                                             0.30                                                                             29.1                                                                             36.3                               Analysis                                                                      43-45                                                                              280     300  3:5 201/157                                                                              325  96.2                                                                             0.35                                     46-48                                                                              285 18200                                                                             303  3:5 204/158                                                                              295  97.7                                                                             0.20                                     49-51                                                                              310     302  3:5 204/157                                                                              440  97.5                                                                             0.22                                     51-53                                                                              385 20460                                                                             302  3:3 205/154                                                                              275  96.5                                                                             0.19                                     Kettle                            26.7  25.7                                                                             41.2                               Analysis                                                                      54-56                                                                              403     300  3:7 197/156                                                                              480  94.7                                                                             0.35                                     57-59                                                                              316 22762                                                                             300  3:5 200/156                                                                              436  95.9                                                                             0.22                                     Kettle                            26.8  15.0                                                                             50.8                               Analysis                                                                      61-63                                                                              368 24442                                                                             300  3:5 202/154                                                                              460  95.0                                                                             0.34                                     Kettle                            26.9  14.9                                                                             50.4                               Analysis                                                                      65-67                                                                              350 26202                                                                             300   3:10                                                                             202/156                                                                              433  96.2                                                                             0.43                                     68-70                                                                               0      300  7:3 219/166                                                                              300  96.9                                                                             0.16                                     __________________________________________________________________________

EXAMPLE 6

This example demonstrates operation of the process for the preparationof high purity product that is free of water and organic lights.Furthermore, the system was shown to run well using a crude feed thatconsisted of 93% isomeric monohydroxy-2,2,4-trimethylpentyl isobutyrates(A), 2.5% of 2,2,4-trimethyl-1,3 pentanediol and 2.6%2,2,4-trimethylpentyl 1,3-diisobutyrate. The diol and diisobutyrate wereadded to determine whether they would have any significant effect on thecatalytic reaction. The system used for this example consisted of a2-liter kettle, 30-tray and 20-tray Oldershaw columns that wereconnected via a liquid takeoff adapter, and a water cooled automaticreflux head.

The crude feed was fed to the 2-liter kettle (initial charge of 1350 g)and a mid-column make (composed mostly of product (B)) was taken 30trays above the kettle, while organic lights and water were takenoverhead (50 trays above the kettle). The column was operated at 300torr using 0.30 wt. % sodium hydrogen sulfate as the acid catalyst. Thecomposition of the mid-column make (98+% product (B)) was excellent asshown in Table 8. The overhead make rate was low when compared to themid-column make rate.

                                      TABLE 8                                     __________________________________________________________________________             Temp. (°C.)                                                                          Overhead                                               Reaction                                                                           Feed                                                                              Kettle/                                                                              Mid-Column                                                                           Make Rate                                                                             Composition of                                 Progress                                                                           Rate                                                                              Mid-Column/                                                                          Make Rate                                                                            (mL/h)  Mid-Column Make                                (hrs)                                                                              (mL/h)                                                                            Head   (mL/h) Organic/Water                                                                         % B                                                                              % D                                                                              % A                                                                              % C                                   __________________________________________________________________________    3-5  327 199/168/120                                                                          --     --      98.8                                                                             0.68                                                                             0  0                                      8-12                                                                              221 200/169/100                                                                          --     --      99.1                                                                             0.37                                                                             0  0                                     Kettle                                                                             --  --     --     --      44.6                                                                             0.86                                                                             18.0                                                                             29.4                                  Analysis                                                                      12-15                                                                              425 202/169/97                                                                           371    40.sup.1 /34                                                                          98.6                                                                             0.65                                                                             0  0                                     15-20                                                                              398 212/168/96                                                                           348    45.sup.2 /33                                                                          97.7                                                                             1.5                                                                              0  0                                     Kettle                                                                             --  --     --     --      13.6                                                                             0.42                                                                             39.3                                                                             40.4                                  Analysis                                                                      21-24                                                                              368 213/168/85                                                                           340    28.sup.3 /30                                                                          98.6                                                                             0.80                                                                             0  0                                     __________________________________________________________________________     .sup.1 58% B, 42% Lights                                                      .sup.2 52% B, 47% Lights                                                      .sup.3 32% B, 68% Lights                                                 

EXAMPLE 7

This example shows operation of the process in the batch mode. Thesystem used for this example consisted of a 40-tray Oldershaw columnequipped with a water cooled automatic reflux head and a 3-liter kettle.The system was charged with 2 kg of monohydroxy-2,2,4-trimethylpentylisobutyrates (A) and 0.30 wt. % NaHSO₄. The results from the batchreaction are summarized in Table 9. With the exception of startup (0-2hours), the reaction is highly efficient (>90%). Near the end of thereaction (14-16 hours), product B distilled overhead in high purity(99%).

                  TABLE 9                                                         ______________________________________                                        Reaction                                                                      Progress Pressure Temp. (°C.)                                                                         Reflux                                                                              Yield                                    (hrs)    (mm Hg)  Kettle/Head  Ratio % B                                      ______________________________________                                        0-2      300      180/90       2:1    7.5                                     3-5      300      180/152      2:1   95.9                                      6-10    300      183/154      3:1   90.6                                     10-13    300      184/162      4:1   93.6                                     14-16    300      198/172      1:2   99.1                                     ______________________________________                                    

EXAMPLE 8

This example demonstrates operation of the process of this inventionusing a crude mixed feed of2-ethyl-2,4-dimethyl-3-hydroxy-hexyl-1-(2-methyl butyrate) and2-ethyl-2,4 dimethyl-1 hydroxy hexyl 3(2 methyl butyrate) (E). This feedalso contained several percent 2-ethyl-2,4-dimethyl-1,3-hexanediol (F)and 2-ethyl-2,4-dimethyl-1,3-hexanediol di(2-methyl butyrate) (G). Aninitial charge of 1482 g of the monohydroxy 2-ethyl-2,4-dimethyl hexyl(2-methyl butyrates) (E) was used together with 3.2 g (0.21%) sodiumhydrogen sulfate catalyst in the reaction system described in Example 1(30-tray Oldershaw column). The reaction system was operated for 34hours with typical results described in Table 10. In addition to theexpected mixture of 2-ethyl-2,4-dimethylhexenyl 1-(2 methyl butyrates)(H) some of the isomeric 2-ethyl-2,4-dimethyl-hexen-1-ols (I)codistilled with the product (H). With this feed, yields to desiredproduct (H) were lower than in Examples 1 to 7, but applicants are stillable to produce product (H) at the conditions of temperature andcatalyst heretofore considered not applicable in U.S. Pat. No.3,408,388.

                                      TABLE 10                                    __________________________________________________________________________    Reaction  Feed       Make                                                     Progress                                                                           Pressure                                                                           Rate                                                                              Temp. (°C.)                                                                   Rate Reflux                                                                            Yield                                           (hrs)                                                                              (mm Hg)                                                                            ml/hr.                                                                            Kettle/Head                                                                          (ml/hr.)                                                                           Ratio                                                                             % H                                                                              % F                                                                              % I                                       __________________________________________________________________________    7-8  152  480 236/186                                                                              260  1/10                                                                              87.3                                                                              4.9                                                                             5.2                                       11-12                                                                              100  280 227/169                                                                              140   4/2                                                                              68.5                                                                             16.5                                                                             8.6                                       28-29                                                                              100   80 196/170                                                                               70  10/2                                                                              75.4                                                                              7.7                                                                             6.8                                       __________________________________________________________________________

What is claimed is:
 1. A process for the production of unsaturated2,2,4-trisubstituted monoesters of the formulas: ##STR10## by thecatalytic dehydration of a saturated 2,2,4-trisubstituted glycolmonoester of the formula: ##STR11## in contact with a catalytic amountof a substantially non-volatile acid catalyst sufficient to catalyze thedehydration reaction at a temperature of from about 170° C. to about270° C., said catalyst being selected from the group consisting ofsodium hydrogen sulfate and potassium hydrogen sulfate, wherein:R ishydrogen or an R' group; R' is (i) an alkyl group having from 1 to about8 carbon atoms, (ii) a cycloalkyl group having 5 or 6 ring carbon atoms,or (iii) an aryl, or aralkyl group in which the aromatic ring is phenylor naphthyl; and R" is (i) hydrogen or (ii) an --OCR' group with theproviso that in Formula I one of the R" groups is hydrogen and inFormulas I, II and III and --OCR' group is always present.
 2. A processas claimed in claim 1 wherein Compound (I) has the formula: ##STR12##and R" is an --OCR' group.
 3. A process as claimed in claim 1 whereinCompound (I) has the formula: ##STR13## and R" is an --OCR' group.
 4. Aprocess as claimed in claim 1 wherein R' is an alkyl group having from 1to about 4 carbon atoms.
 5. A process as claimed in claim 1 wherein Rand R' are methyl.
 6. A process as claimed in claim 1 wherein theunsaturated 2,2,4-trisubstituted monoesters is a mixture of theethyldimethylhexylene 2-methyl butyrate isomers.
 7. A process as claimedin claim 1 wherein the dehydration reaction is carried out at atemperature of from about 180° C. to about 250° C.
 8. A process asclaimed in claim 1 wherein the acid catalyst is sodium hydrogen sulfate.9. A process as claimed in claim 1 wherein the acid catalyst ispotassium hydrogen sulfate.
 10. A process as claimed in claim 1 whereinCompound (I) is 3-hydroxy-2,2,4-trimethylpentyl isobutyrate.
 11. Aprocess as claimed in claim 1 wherein said unsaturated2,2,4-trisubstituted monoester is a mixture of the unsaturated isomersof 2,2,4-trimethylpentenyl-1-isobutyrate.
 12. A process as claimed inclaim 1 wherein the saturated 2,2,4-trisubstituted glycol monoester is3-hydroxy-2,2,4-trimethylpentyl isbutyrate and the unsaturated2,2,4-trisubstituted monoester is a mixture of2,2,4-trimethyl-3-pentenyl isobutyrate and 2,2,4-trimethyl-4-pentenylisobutyrate.
 13. A process as claimed in claim 1 wherein the saturated2,2,4-trisubstituted glycol monoester is 3-hydroxy-2,2,4-trimethylpentylisbutyrate and the unsaturated 2,2,4-trisubstituted monoester is amixture of 2,2,4-trimethyl-3-pentenyl isobutyrate and2,2,4-trimethyl-4-pentenyl isobutryate, the acid catalyst is sodiumhydrogen sulfate and the temperature is from about 180° C. to about 250°C.
 14. A process as claimed in claim 1 wherein the saturated2,2,4-trisubstituted glycol monoester is 3-hydroxy-2,2,4-trimethylpentylisobutyrate and the unsaturated 2,2,4-trisubstituted monoester is amixture of 2,2,4-trimethyl-3-pentenyl isobutyrate and2,2,4-trimethyl-4-pentenyl isobutyrate, the acid catalyst is potassiumhydrogen sulfate and the temperature is from about 180° C. to about 250°C.